Some people lose themselves in the crazy. I'm curious if he has voices. And I'm curious what the voices tell him. The voices tell many things to be honest. They trick you into things. For awhile they tried to make me think I was somehow the reincarnate of God. I never believed it. I don't believe in reincarnation. I'm a biology background and very science minded. But I didn't believe in God either. But I do now, because of my voices. I had a disney fairytale psychosis where I fought ultimate evil and in order to defeat ultimate evil I had to kiss a girl.
If you want to help him, ask him questions, probe him, ask him why he thinks that, what made him think that, when he thought that, where he thought that, ask him do the voices promote it, what kind of signs do you see? And I would just use logic to take apart his experiences and make him based in reality. Not all schizophrenics are the same by the way. The reincarnate of prophet delusion is common, bring that up with him, what makes him stand out from others? Without promoting him, ask him, if you are this so called reincarnate, what do you feel your duties and obligations are? And I would just reason and rationale to logically ground him in reality.
I would recommend him to r/schizophrenia and r/psychosis for reading up on other peoples experience. Perhaps that will help him ground in reality. I will say this, experiencing the voices can be very surreal and they can make you think a lot of things. I've just written down what I can best recollect of my experiences with the voices. If you read my story. You probably think I'm crazy as well. Well, I've tried explaining this once before but every brain generates the world around them via interpreting electrical signals in your brain. Your vision is electrical signals. Your sound is electrical signals. It's all in your head being processed and formatted into what you experience of reality. Voices and imagination is also electrical signals in the brain. You are essentially your thoughts, you are living continuum of thoughts with visual and auditorial reminders every day. Psychosis takes the universe you generate inside your head and your thoughts and warps them. Altering the electrical signals you fire, sometimes permanently. Which isn't a bad thing, I turned the universe I generate in my head into a simulation and used that to work with the voices for advancement of science, dream pioneering, to create a permanent dream world to act as an afterlife or hub of life for everyone to live in. I want to save the world. Thats my schizophrenic motto. So in your friends head, he may really experience the feeling of being that reincarnate of Jesus. Yet again, reincarnation is easy to dismantle. We all grow from an egg and sperm, into primitive streak and develop into the biological entities that our dna blueprint instructs. The only logical argument he can make is he has the spirit of jesus in him. Well, a lot of people believe that also. Ask him to make some prophet predictions and write down prediction dates. When time passes and they eventually don't happen that will further disprove your friends skewed view of reality.